Paper coating



Aug. 18, 1936. gOYER ET AL 2,051,403

PAPER COATING Filed July 16, 1930 2 Shets-Sheet 1 i 9,1 j rmerzivr'sZkeiru7wI 7 y;

Aug. 18, 1936. s. BOYER ET AL PAPER COATING Filed July 16, l9d 2Sheets-Sheet .2

jilk'fillwifif .Sylaasier Faye? Patented Aug. 18, 1936 UNITED STATESPATENT .OFFICE PAPER COATING sachusetts Application July 16, 1930,Serial No. 468,260

16 Claims.

This invention relates to the art of coating paper and is here presentedin its aspects of method and mechanism. The main object of the inventionis to coat paper more smoothly, and more expeditiously than by themethods heretofore generally practiced, whether the paper be coated onone side at a time, or on both sides simultaneously; obviously thisobject will be best served by the latter mode, and therefore sundryfeatures of invention are concerned with this preferred mode ofoperation.

Any of the coating compositions employed in paper making may beemployed; a typical example is a composition of china clay and starch inwater. To secure the full advantage of the improvements herein to bedescribed, however, the composition should be decidedly more viscousthan those generally employed in normal paper mill practice,- so thatthe time required to evaporate the water content down to the optimumpercentage for the final coat forming and smoothing operation may bereduced to a minimum; and so that the residual coating left on the papershall, as it leaves the smoothing instruments, be of such firmconsistency that it will not flow, even if the paper surface bevertical. In a coating machine such as that presently to be described, acomposition of viscosity 600 to 800, as measured by the MacMichaelviscosimeter with its disc rotating at from to 50 turns per minute, hasbeen found satisfactory.

In the drawings hereto annexed, of a coating machine exemplifying, instructure and mode 'of operation, the inventions herein claimed,

Fig. 1 shows the coating machine, partly in side elevation, partly invertical section;

Fig. 2, the squeeze-rolls and coating-wipers, in detail and on arelatively large scale;

Fig. 3, the coating-wipers, in detail and on a still larger scale; and

Fig. 4, a detail of the back-scraper attached to a coating-wiper, on thesame scale as Fig. 2, viewed in the direction indicated by the dottedarrow in Fig. 2.

wheel l8; sprocket chains l9,

Coating material is the surface of the liquid coating material, thenceupward between the squeeze-rolls R, R, which are adjusted to reduce theload of coating material adhering to the paper to a predeterminedregular quantity. From the rolls R the paper P passes over the wipers W,W, in succession; these wipers are horizontally adjusted so that thepaper, with its adhering coating material, is stressed against theworking faces of the wipers (see Figs. 2 and 3). The wipers W, W aremounted at each end on bars 3, 4, which are vertically adjustable inslots 5, 5, by means of nuts 6, 6. The horizontal adjustment of thewipers is obtained by means of slots 1, l, and nuts 8, 8 (see also Figs.2 and 4) From the wipers W, W,-the paper passes upward into, through,and out of, the box 13. Drying air is blown against the coated paper bythe airchests 9, 9; the air eduction pipe is shown at H]. Steam coils,indicated by 23, may also be provided. After emergence from the box B,the paper P, on which the coating material has been set by drying,passes over rolls ll, I2, and i3, to the draft roll l4, which ispreferably a felt covered roll, over roll 16, to the winding-up roll ll.Rolls l3 and I6, and the pressure roll l5, provide for effective draftaction by roll I4 on the paper strip P.

Power is applied to the shaft of the sprocket 20, 2|, and 22 drive therolls R, R, H and l4.

The salient instrumentalities in the coating machine, above generallydescribed, are the wipers W, W, and their immediate adjuncts. Each wiperconsists of a metal bar, made rigid by the provision of integral webs(w, w); hard bronze has proved to be an excellent material of which tomake these bars. The active surfaces of the wipers are (generallyspeaking) cylindrical in character, and preferably comprise surfaces a,of major radius a, and b, of minor radius b (see Fig. 3); a major radiusof inch and a minor radius of- /64 inch has been found suitable.Experiment has demonstrated that relatively gradual approach to, andrelatively abrupt departure from the wiper-surfaces by the coated papersurface, constitutes a preferable condition and conduces to regularlygood results, and that while a working compromise can be reached by theuse of a cylindrical working face of one radius (intermediate betweenthe major and minor values above recommended), such a compromisecondition is not wholly dependable.

The wipers W and W are, by means of the slots 1, l, and set-nuts 8, 8,adjusted horizontally so that the moving strip of paper is drawn againsteach wiper-face with pressure sumcient The vertical spacing, thehorizontal'overlap,

and the distance from the nip of the squeezerolls to the lower wiper,are all variable, and will be determined in practice to meet variationsin the character and consistency of the coating material, the weight ofcoating to be laid on the paper, the quality and type of the papenandthe rate'of paper-travel; perhaps also, the atmospheric conditions.Adjustments should be made to the end that'the coating material, whilestill sufiiciently fluid to be in part wiped back and removed from thepredetermined residue which is to be permanently fixed on the paper,shall be of such consistency as not to run by its own weight after itsthickness has been reduced by the action of the wiper.

The squeeze-rolls R, while contributorily useful in regulating theweight and thickness of coating material which is to be acted on finallyby the wipers. may be dispensed with, though this is not recommended.

Theoretically, and if perfectly uniform smooth consistency of coatingmaterial couldbe guaranteed, the two wipers W and W might be placed inopposition to each other; their arrangement in succession of operationis advantageous as providing that each shall be opposed only by thetension of the. unsupported paper web or strip, for automatic adjustmentof the thickness of the coating in response to the plastic insistence orviscosity ofthe coating, and for relief if and when a lump of coatingmaterial or other abnormal object is carried into the load of coating onthe paper. With directly opposed wipers, also, it is difllcult to obtainand maintain that nice adjustment which is indispensable if the finalcoating layer on either side of the paperis to be uniform in thickness.

With the described preferred mode of vertical spacing of thesuccessively operating wipers, the

coating'load C '(Fig. 2) creeps around the edges of the paper P to theopposite side and marginally overlies the coating C after the latter hasbeen wiped down to its final weight by the wiper W. A back-scraper(Figs. 2 and 4) is provided at each end of wiper W to remove suchcoating mate-'- rial. This instrument consists of a metal plate D,deeply notched at d to form the scraping finger d, 'and held in place onthe upper surface of the wiper W by means of a stout holdingdownleaf-spring G, secured to the upstanding flange w. The finger d is madelong enough to reach and remove any coating material which has creptaround the edge of the paper. I only of the necessary two back scrapersis shown in the drawings.

The operation of the above-described coating machine is as follows:

The paper strip,.rising from the pool of coat- I ing material in thetank T, carries with it a layer of viscous liquid coating, on each side;these layers are first reduced in thickness by the action of thesqueeze-rolls R, R,-which leave One layers in excess of thepredetermined final weight of coating still adhering to and carried bythe paper. The paper is drawn against the smooth curved acting face ofwiper W, making relatively gradual approach as the viscous coatingyields to displacement by the wiper under the resultant force of thelongitudinal tension on the paper strip to that part of the wiper facewhich has the curvature of major radius.- This radius may be very large,even to infinity. The excess of still fluid l coating material is wipedback by the wiper, a poo1so to speakof coating material forms be low theline of initial pressure between the longitudinally tense paper andwiper-face, and from this pool the excess flows back over the paper 1strip to the squeeze-roll beneath, by which it is carried into the tank.By reason of the upward inclination of the lower side of the wiper, thecoating material accumulating between the wiper-face and the paper cannot run back on to 2 the wiper and dry there, but must flow or drip downto the squeeze-roll. The action of the portion of the wiper-surface ofmajor radius is to wipe back liquid coating material, reducing thethickness of the layer progressively, until the 2 layer attains thatdegree of thinness at which force of adhesion to the paperovermasters-the wiping-back eflect of the wiper. After the paper striphas passed this point where the wiper ceases to remove fluid materialfrom the layer, the wiper 3 surface exerts a frictional smoothing effecton the residue which clings to the paper, until the paper reaches thepart of the wiper face which hasjthe minor radius of curvature. Fromthis more abruptly curved surface the paper andits 3 residue of coatingmakes an abrupt departure, of which the effect is to leave the coatingsmooth, free from ridges, depressions, pits, or pimples.

This residue, which ultimately forms the coating on the finished paper,while still containing water, to be subsequently evaporated, is of suchconsistency, and so closely adherent to the paper, that on leaving'thewiper surface, it is fixed, and incapable of internal flow in responseto gravitative force. The performance of the wiper W' i on the otherside of the paper is in all respects like that of wiper W. Withanyselected horizontal adjustment of the wipers in relation to eachother and the paper strip, each wiper will, by rotative adjustment, begiven that inclination which will ensure the approach of the paper to,and its departure from, the wiper surfaces in the manner abovedescribed. After the coating has been thus treated, the passage of thepaper strip through the drying box B sets the coating and the process iscompleted.

\The curvatures of the wiper faces need not be circular (in section)that of the wiping portion, represented by the surface a in Figs. 2 and3 may be of any conformation consistent with perform- 6 ance of thedesired function, viz: removing or wiping back fluid coating material inexcess of that which, by its adhesion to the paper effectively resistsdisplacement by said wiping action;

3 that of the portion represented by the surface b 6 may be of anyconformation between two limiting conditions, viz: a sharp edge, whichexperiment has demonstrated to .be liable to produce ridges in theresidual coating, and a surface of large-radius curvature, from whichthe departure 7 of the coated paper surface is so gradual as to permitadhesions to form between the said wiper surface and the coatingmateriaL'with consequent production of pimples or pits, orboth, on thecoating, which, under the conditions pre I scribed, is incapable offully healing such blemishes by internal flow.

The weight of coating per unit area of paper is regulable by adjustmentof the following factors: First, the consistency or viscosity of thecoating composition; second, the time of exposure of applied coatingmaterial to evaporative agencies before subjecting it to the action ofthe wiper; third, the stress of the paper sheet against the working faceof the wiper, and fourth, the angle of inclination of the curved surfaceof major radius of the wiper, relative to the plane of the path oftravel of the web or paper sheet. It is here assumed that the rate ofmovement of the paper strip is a constant, and at the maximum foundpracticable. When constant values of the three variables above named aredetermined and maintained, the weight of coating material per unit ofpaper area in the finished product will be the solid residue of thatfraction of the originally applied layer of fluid coating which, byforce of adhesion to the paper effectively resisted displacement by thewiper.

Since return-flow of the wiped-back excess of a fluid layer of coatingis a characteristic of this method, and of the operation of a coatingmachine exemplifying the principle of the invention, the direction ofthe paper-strip movement, at the point of wiper-application shouldpreferably be upward and substantially vertical, that is to say, adirection consistent with gravitative back-flow of the removed excess ofcoating composition. The word vertical (with its correlatives) is hereinused in this general sense, and not necessarily in the strict sense,although for the preferred method of simultaneously coating both sidesof a paper strip, truly vertical movement thereof is the best adapted.

Nevertheless, while the upward and substantially vertical movement ofthe paper strip to and through the system of coating instruments appearsto be on the whole preferable, suitable means for applying coating, andremoving excess coating, while performing the characteristic wiping andsmoothing operations above described, may readily be contrived bypersons skilled in the art and made familiar with the principles onwhich the herein described apparatus works, to adapt it either todownward vertical movement of the paper strip, or to movement in ahorizontal direction.

We claim:

1. In a paper coating machine, paper-strip moving means, means to applyfluid coating composition to the paper, a wiper mounted to press againstthe coated surface of the moving paper at a point in the travel thereofwhere the composition thereon is still fluid, said wiper furnished witha surface of major radius to which the paper approaches, and a curvedsurface of minor radius from which the paper departs, whereby a portionof the composition applied to the paper is wiped back and an immobileresidue left adherent to the paper, and means for setting said adherentresidue.

2. In a paper coating machine, paper-strip moving means, means to applyfluid coating composition to both sides of the paper, two curvedsurfacedwipers mounted to press in succession against opposite coated surfacesof the paper strip while the composition thereon is still fluid,backscrapers applied tothe margins of the paper strip on the sidethereof treated by the first wiper to act thereon, whereby a portion ofthe composition applied to the paper is wiped back and an adherent toboth sides of for setting said adherent immobile residue left the paper,and means residue.

3. In -a paper coating machine, paper-strip moving means, means to applyfluid coating composition to both sides of the paper, two wipers mountedto press in succession against opposite coated surfaces of the paperstrip while the composition thereon is still fluid, each wiper furnishedwith a surface of major radius to which the paper approaches, and acurved surface of minor radius from which the paper departs, whereby aportion of the composition applied to the paper is wiped back and animmobile residue left adherent to both sides of the paper, and means forsetting said adherent residue.

4-. In a paper coating machine, paper-strip moving means, means to applyfluid coating composition to both sides of the paper, two wipers mountedto press insuccession against opposite coated surfaces of the paperstrip while the composition thereon is still fluid, back-scrapersapplied to the margins of the paper strip on the side thereof treated bythe first wiper to act thereon, each wiper furnished with a surface ofmajor radius to which the paper approaches, and a curved surface ofminor radius from which the paper departs, whereby a portion of thecomposition applied to the paper is wiped back and an immobile residueleft the paper, and means residue.

5. In a coating machine of the type having means for moving a web underlongitudinal tension and means for applying a fluid coating compositionto one of its faces, a wiper mounted to press against the coated surfaceof the moving and tense web, said wiper having a curved surface of majorradius to which the web approaches, and a curved surface of minor radiusfrom which the web departs, whereby a portion of the coating compositionapplied to the web is wiped back and an immobile residue left adherentto the face of the web.

6. In a coating machine of the type having means for moving a web andmeans for applying a fluid coating compositionto one of its faces, awiper mounted to press against the coated surface of the moving web inopposition to the tensile stress on the web, said wiper having a curvedsurface of major radius to which the web approaches, and a curvedsurface of minor radius from which the web departs, whereby a portion ofthe coating composition applied to the web is for setting said adherentwiped back and an immobile residue left adherent to the face of the web,and means for adjusting said wiper to varythe angle of inclination ofits curved surface of major radius, relative to the plane of traverse ofthe web, whereby to regulate the amount of coating left on the web.

'7. In a coating machine of the type having means for moving a websubstantially vertical path and .means for applying a fluid coatingcomposition to the face of the moving web, a wiper mounted to pressagainst the coated surface of the moving web, said wiper having a curvedsurface of major radius to which the web approaches, and a curvedsurface of minor radius from which the web departs, whereby a portion ofthe coating composition applied to the web is wiped back and an immobileresidue left adherent to the face of the web, and means for adjustingthe horizontal and angular position of said wiper, relative to the pathof the moving web, whereby the'tension on and the adherent to both sidesof a in a tense state in a by surplus coating material is continuallyfed 4 amount of coating applied to said web may be regulated.

8. In a coating machine of the type having means for moving a web in asubstantially vertical path and means for applying a fluid coatingcomposition to the face of the moving web, a wiper mounted to pressagainst the coated surface of the moving web and hold the-same under'tension, said wiper having a curved surface of major radius to which theweb approaches, a curved surface of minor radius from which" the webdeparts, and an under surface inclined upwardly from the path of themoving web, whereincreasing wiping pressure followed immediately by aless gradually decreasing wiping pressure.

10. Method of coating paper, comprising applying a layer of fluidcomposition to the surface of a paper strip, moving the coated paperstrip longitudinally, under tension, and subjecting the sameto a wipingaction comprising a gradually increasing wiping pressure foll edimmediately by a less gradually decreasing'wiping pressure, and leavingadherent to the paper a coating of an immobile residue of a thicknessdetermined by the tension of the strip and the viscosity of the coating.

11. Method of coating paper, comprising applying layers of fluid coatingcomposition to the two surfaces of a paper strip, moving the coatedpaper strip longitudinally, under tension, and subjecting the same, onboth sides of the sheet, to a wiping action comprising a graduallyincreasing, followed immediately by a less gradually decreasing wipingpressure.

12. Method of coating paper, comprising applying layers of fluid coatingcomposition to the two surfaces of a paper strip, moving flie coatedpaper strip longitudinally, under tension, and subjecting the same, onboth sides of the sheet, to a continuous wiping action comprising agradually increasing, a sustained, and a less gradually decreasingwiping pressure.

13. Method of coating paper, comprising applying a layer of fluidcoating composition to the surface of a paper strip, moving the coatedpaper strip longitudinally, under tension, and subjecting the same, onthe coated side of the sheet, to a continuous wiping action comprising agradually increasing, a sustained and a less gradually decreasing wipingpressure.

14. Method of coating paper, comprising applying a layer of fluidcoating composition to the surface of a paper strip, moving the paperlongitudinally under tension, diverting the path of the paper firstthrough a curve of major radius and then through a curve of minor radiusand simultaneously wiping back from said layer a portion of the fluidcoated composition, leaving adherent to the paper a coating of immobilecoating residue.

15. Methodof coating paper, comprising applying a layer of fluid coatingcomposition to the surfacepf a paper strip, moving the paperlongitudinally under tension, diverting the path of the paper firstthrough a curve of major radius and then through a curve of minor radiusand simultaneously wiping back from said layer a portion of the fluidcoating composition, leaving adherent to the paper a coating of immobilecoating residue of a thickness determined by the tension of the stripand the viscosity of the coating.

. leave residual coating composition in the surface of the paper, saidleveling device having a radius of curvature of not more than inch atthe point where the paper leaves the scraper and a greater radius ofcurvature at the point where the paper first contacts the levelingdevice.

SYLVESTER BOYER. LE CLARE F. PARMEN'I'ER.

16. In a paper treating apparatus, means for

